The invention relates to a radio communication method at high frequency between a base station with N antennae and a mobile phone, and a base station for implementing same.
It can be applied to digital cell telephone systems in which one and the same station is provided with a network of antennae allowing it to serve a plurality of mobile phones in a cell.
In such a station, during transmission, the signals to be applied to each antenna are synthesised on the basis of the signal intended to reach the mobile phone.
To achieve this, in the transmission chain of each antenna a number of digital processes generally produce samples representing these signals. Then, by means of digital-analog conversion and modulation to the carrier frequency, each signal is synthesised then simplified and applied to the appropriate antenna of the network.
The complexity of the calculations necessary to synthesise these patterns, and the cost of the digital-analog conversion circuits and of modulation, increase with the number of antennae in the network.
Hereinafter, the term multi-sensor transmission device shall be used to refer to the whole of the circuits which produce the signals applied to each elementary antenna for transmission to the mobile phone.
At reception, in analog mode, the reception chain of each antenna feeds the signals received by this antenna into an intermediary frequency or the base band. The signals are then sampled and subjected to analog-digital conversion. The samples are then processed by digital processes to extract the information transmitted by the mobile phone.
The complexity and the cost of the circuits of the reception paths again increase with the number of antennae in the network.
Hereinafter, the term multi-sensor reception device shall be used to refer to the whole of the circuits which process the signals received from the mobile phone in order to extract the information transmitted.
The network of antennae may feature any geometry considered appropriate. In particular, the antennae may be disposed in line and regularly spaced. In this event, they are preferably directional, and their lobes point in the orthogonal direction to the right of which the antennae are aligned.
The antennae may equally be disposed in a circle and regularly spaced. In this event, the antennae are likewise preferably directional and their lobes point in a radial direction towards the outside of the circle on which they are disposed.
The invention applies likewise to a network of antennae presenting a regular polygon geometry such as an equilateral triangle, a square, a pentagon, a hexagon, etc., with antennae spaced regularly along its sides.
The objective of the invention is to reduce the complexity of the calculation and the cost of the processing procedures carried out by a base station provided with a network of antennae.
In order to achieve this objective, the invention proposes a method of communication between a base station consisting of a network of N distinctive antennae, N being a whole number greater than 1, and at least one mobile telephone, characterised in that:
(a) The directions of arrival and the power values of the radio-electrical paths are estimated at the base station;
(b) A principal direction of arrival is determined for said mobile telephone of said radio-electrical paths at the base station;
(c) M antennae are selected, M being a whole number less than N, the individual reception lobes of which have directions contained in an angular sector centred on the principal direction of arrival;
(d) Only the signals which are received by the M antennae selected and deriving from the mobile telephone are processed.
For the transmission according to this process,
(e) M antennae are selected, of which the individual transmission lobes have directions contained within angular sector centred on the principal direction of arrival;
(f) Only the signals to be transmitted by the M antennae selected are synthesised.
The invention likewise proposed a radio communications base station with mobile telephones, comprising a network of different N antennae, N being a whole number greater than 1, and K reception or transmission chains, K being a whole number less than Nxc3x97L, where L is the number of simultaneous communications, characterised in that it comprises:
Means of assessing the directions of arrival and the power values of the radio-electrical paths at the base station;
Means of determining, for a given mobile telephone, a principal direction of arrival of the radio-electrical paths at the base station;
Means of selection of M antennae, M being a whole number less than N, of which the individual reception or transmission lobes have directions contained within an angular sector centred on the principal direction of arrival;
Means of switching, affecting, for each communication, M reception or transmission chains at the M antennae previously selected.
In a specific embodiment of the invention, the principal direction referred to heretofore is the direction of arrival for which the radio-electric power received or transmitted and reaching the mobile telephone (according to whether it is in reception or transmission mode) is the greatest.
In another specific embodiment of the invention, the principal direction referred to heretofore is the barycentre r of the directions of arrival of the different radio-electric paths, defined as follows:   r  =            (                        ∑                      i            =            1                    J                ⁢                  xe2x80x83                ⁢                              p            i                    ·                      a            i                              )        /          (                        ∑                      i            =            1                    J                ⁢                  xe2x80x83                ⁢                  p          i                    )      
where i is a whole number,
where J is the number of radio-electrical paths identified, where ai is the angle formed by the ith radio-electrical path in relation to the direction of the path having the greatest radio-electrical power value, and
where pi is the radio-electrical power of the ith path.